Field of the Invention and Related Art Statements
The present invention relates to a ceramic joined body preferably used for a package of integrated circuits, wherein a metalizing layer formed on a surface of an aluminum nitride member and a metalizing layer formed on a surface of a low temperature fireable insulation substrate are joined with each other through a solder used under high temperatures.
Usually, as to a package substrate used for an IC package on which semiconductor chips having high generation of heat are installed, aluminum nitride (AlN) having a high heat conductivity has been used. However, since AlN has a large dielectric constant such as .epsilon..apprxeq.8.8, there is a drawback that signal propagation characteristics are deteriorated. Moreover, since a firing temperature of AlN is high, it is necessary to use metal materials having high melting points such as tungsten (W) and molybdenum (Mo) as wiring conductors. In this case, since the wiring conductors made of the metal materials mentioned above have a high resistivity, there is a drawback that a signal propagation delay of a wiring substrate becomes large and a high integration of the wiring substrate can not be realized.
To eliminate the drawbacks mentioned above, there has been proposed a method such that an aluminum nitride member having high heat conductivity is compounded with an insulation substrate fireable at low temperatures (for example, crystallized glass or glass-ceramic composite body) which can use a wiring conductor having a low resistivity such as Cu, Ag, Au, Ag-Pd.
In order to connect the AlN substrate and the insulation substrate fireable at low temperatures, there has been known a method of forming a metalizing layer made of W and/or Mo on the AlN substrate, forming a metalizing layer made of copper, nickel etc. and connecting the AlN substrate and the insulation substrate fireable at low temperatures through solder used under high temperatures, such as silver solder (for example, 72 wt. % Ag-Cu eutectic alloy, melting point: 780.degree. C).
However, in the method mentioned above wherein the AlN substrate and the insulation substrate fireable in at low temperatures are brazed with each other through the metalizing layer by using the solder used under high temperatures, residual heat stresses due to the brazing operation remain in the substrates. Therefore, the metalizing layer is peeled off from the side of the insulation substrate fireable at low temperatures having a low flexural strength or the composite body is easily broken from the metalizing layer. Therefore, there is a drawback that a sufficient connection strength between the AlN substrate and the insulation substrate fireable at low temperatures can not be obtained.
To eliminate drawback mentioned above, the Japanese Patent Application Laid-open Publication No. 62-290158 discloses a composite body between materials having high heat conductivity such as AlN, SiC, etc. and alumina, mullite or a low temperature fireable substrate. In this case, a spacer made of Cu/W, W, etc., which has an intermediate thermal expansion coefficient between those of the high heat conductive materials and the low temperature fireable substrate, is arranged therebetween so as to prevent the generation of cracks and flexures due to the residual stresses generated during the high temperature brazing operation.
However, even if the residual stresses are reduced by using a predetermined spacer as mentioned above, a sufficient connection strength still can not be obtained.
Further, in U.S. Pat. No. 4,695,517, a first layer including W, Mo and a second layer including only W, Mo are co-fired with an AlN substrate so as to increase a connection strength between a metalizing layer and the AlN substrate.
However, in technique disclosed in the U.S. Pat. No. 4,695,517, since use is made of W, Mo as conductors in the metalizing layer, it is not applicable to substrates fireable at low temperatures.